Neurons communicate by releasing neurotransmitters, which diffuse to neighboring cells causing an effect by interacting with a receptor. Changes in neurotransmitter levels within the extra cellular space are an indication of the messages sent between neurons. Measurement of these concentration dynamics in vivo is an important means of understanding neurotransmission and ultimately the brain, brain diseases, and behavior. Present methods for monitoring neurotransmitters in vivo involve sensors or sampling techniques coupled with analysis of fractions. Sensors are powerful yet limited to measuring one compound at a time. Furthermore, sensors for just a few of the over 100 neurotransmitters have been developed. Sampling approaches are limited by temporal resolution of a few minutes whereas neurotransmitter concentrations change on the second time scale. In addition, the large size of sampling probes precludes measurement in many brain regions. The objective of this work is to develop methods of monitoring many neurotransmitters with physiologically and behaviorally relevant temporal and spatial resolution. In this proposal a microfabricated electrophoresis system will be coupled to a microdialysis probe to accomplish high-resolution monitoring of amine neurotransmitters. A novel microsampling probe with over 500-fold better spatial resolution than microdialysis will be developed. Neuropeptide analysis will be improved by developing sampling probes with improved collection efficiencies. In addition, improved sensitivity for neuropeptide measurements will be obtained by interfacing miniaturized capillary chromatography columns to mass spectrometry. The methods will be applied by collaborating with several neuroscience groups for investigation of: 1) taurine/dopamine neurotransmission in ethanol addiction, 2) glutamate/ascorbate interactions in mice engineered to develop Huntington's disease, 3) the in vivo neurochemical effects of an enkephalinase inhibitor (a novel anti-depressant), and 4) the neurochemical signals in sleep.